Bromfield is located in NW Cumbria, in the ward of Allerdale below Dewent (i.e. Allerdale north of the river Derwent). The present church comprises a nave with N aisle, and a long rectangular chancel. Built off of the S side of the chancel is a chantry chapel, founded in 1395 (restored in 1925). The N transept/chapel was rebuilt in 1861 as a private family chapel. Built in front of the Romanesque S nave doorway is a later porch. Restorations on the church were undertaken in 1861-2, 1893-4 and 1926. The 12th-century church appears to have been aisleless with a shorter chancel than at present. The S doorway remains from this early church, as do sections of carved stones flanking the chancel arch, which was rebuilt in the late-14th century. Several medieval carved grave covers, a few of which are likely to be of 12th-century date, are kept inside the church. Two cross heads, which had been re-used in an outbuilding of the vicarage, are also documented, but the building no longer remains and the present location of the stones, if they still exist, has not been found.

St Kentigern (nicknamed St Mungo) was active in the area in the later-6th/early-7th century. A number of churches in Cumbria and Scotland are named after him. There was no Domesday record made for this part of England, but early carved stones, the earliest of which is believed to date from the 10th century, have been found in the church fabric and churchyard at Bromfield. However, the first actual reference to the church only comes in the 12th century, when Waldeve, son of Gospatric, gave the advowson and patronage of it to St Mary’s Abbey in York. It continued to be owned by St Mary’s until 1302, when the bishop of Carlisle was allowed to appropriate the vicarage of Bromfield, Bromfield falling within the boundaries of the the bishop of Carlisle. The church continued in the possession of St Mary's, York throughout the rest of the medieval period. There remained, however, some confusion over responsibilities for the church fabric, as shown in 1392 when it was alleged that the church should be repaired by St Mary’s Abbey; it was decided instead that it was the vicar’s duty. Parts of the church seem to have been rebuilt at this time. St Mary’s Abbey in York was founded in the late-11th century, while the bishopric of Carlisle only came into being in 1133 (the bishopric was vacant from 1156/7 until 1203).

The manor of Bromfield was itself given by Waldeve to Melbeth, his physician, Melbeth and his heirs taking the name ‘de Bromfield’. Various spellings of Bromfield in medieval documents have caused some confusion regarding the history of the church and manor. Although Melbeth received the manor, Waldeve reserved the advowson of the church for himself. This allowed Waldeve to soon after give the church and its advowson to St Mary's Abbey, York.

It has been noted by many people that the S doorway tympanum appears to have been cut from an earlier hogback monument, evidenced on the interior where the upper part of the tympanum is indented (showing just the outlines of earlier carving) and does not fit the larger space of the arch (unlike on the S face of it). The 12th-century chequerboard decoration on the S face of the tympanum is found elsewhere in the old county of Cumberland at such places as St Peter's Church, Kirkbampton (on a capital of the chancel arch); St Bridget's Church, Brigham (on a loose facetted voussoir); and St Cuthbert's Church, Plumbland (on four facetted voussoirs re-used in the vestry fireplace). It can also be found much earlier in the wider region, as on the cross at Bewcastle.

Bracelet-headed grave covers are not easy to date and those at Bromfield are no exception. Ryder suggests a 'late-12th- or 13th-century' date for two of the bracelet-headed grave covers set against the W interior wall (A and B). However, for the top fragment of grave cover with carving very similar to (A) Ryder gives a date of 'later 13th-century'. There are other related bracelet-headed grave covers, for which Ryder gives a variety of dates no earlier than the late-12th century. Some of these were not found when the present author visited the church. For grave cover (C), which is certainly later stylistically than the others on the W wall, Ryder gives a date of 'later 13th century'.

For grave cover (D), with a cross enclosed in a circle, Ryder states that it may date from the 'later 12th century'. It is, however, the small coped grave cover which receives most attention from Ryder, who says it is 'probably of later 12th century date' and 'of some importance'. The foliate decoration carved on one end, with long stems off of which emerge side leaves, can be compared elsewhere within Cumberland at such places as on the N doorway capitals of the church at Bowness-on-Solway, the capital inside the W porch of the church in Harrington, and on the fragments of the baptismal font found in the walling of St Bridget's Church in Beckerment. Two fragments of lost stones, including the cross with fluted arms, said by Ryder to have been built into a stable wall, were sketched by Blair in 1898, which Ryder also discusses. He states that the cross with fluted arms is probably 12thc., as well as another which he draws as a simple cross with plain but fluted arms meeting at the centre in a circle. The cross carved with decorated, fluted arms can be paralleled in general terms with other crosses in the north of the UK, for example at St Machar's Church in Aberdeen, St Helen's Church in Kelloe, Durham Cathedral (kept in the lapidarium), and St Modan's Church in Falkirk, all of which are likely to date from the later-12th century or from about 1200.

The fragments built into the Chancel Arch wall appear to be sections of stringcourses that would originally have run across more of the wall.

Reference to a 12thc. baptismal font is mentioned in certain modern texts, but this is incorrect. All of the present baptismal font is post-12thc. A medieval piscina also survives (now in the vestry), but this, too, is later than the 12thc.